powerpc/time: Remove generic_suspend_{dis/en}able_irqs()

Commit d75d68cf ("powerpc: Clean up obsolete code relating to
decrementer and timebase") made generic_suspend_enable_irqs() and
generic_suspend_disable_irqs() static.

Fold them into their only caller.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c3f9ec9950394ef939014f7934268e6ee30ca04f.1630398566.git.christophe.leroy@csgroup.eu